Field of the Invention
The present invention relates to a zoom lens and is suitable as an image pickup optical system of an image pickup apparatus such as a digital still camera, a video camera, a TV camera, or a monitoring camera.
Description of the Related Art
In recent years, there has been a demand for highly-functional and small image pickup apparatus. Further, as an image pickup optical system to be used in those apparatus, such a zoom lens has been demanded that has a short total lens length, a high zoom ratio, and high optical performance over an entire zoom range. As a small zoom lens having a high zoom ratio, there is known a positive-lead type zoom lens in which a lens unit having a positive refractive power is arranged at a position closest to an object side.
In Japanese Patent Application Laid-Open No. 2010-032702, there is disclosed a zoom lens including, in order from an object side to an image side, five lens units respectively having positive, negative, positive, negative, and positive refractive powers, the zoom lens being configured such that an interval between adjacent lens units is changed during zooming. In Japanese Patent Application Laid-Open No. 2013-152374, there is disclosed a zoom lens including, in order from an object side to an image side, a first lens unit to a fourth lens unit respectively having positive, negative, positive, and positive refractive powers, in which all of the lens units are configured to move during zooming. In Japanese Patent Application Laid-Open No. 2012-47814, there is disclosed a zoom lens including, in order from an object side to an image side, a first lens unit to a sixth lens unit respectively having positive, negative, positive, positive, negative, and positive refractive powers, the zoom lens being configured such that an interval between adjacent lens units is changed during zooming.
In order to achieve downsizing and higher resolving power of the positive-lead type zoom lens described above, for example, it is effective to increase a refractive power of the second lens unit having a negative refractive power, which has a strong magnification-varying action. However, when the refractive power of the second lens unit is simply increased, the occurrence of various aberrations is increased in the second lens unit and it becomes difficult to obtain high optical performance over the entire zoom range.
In order to reduce various aberrations that occur due to an increase in zoom ratio while downsizing the zoom lens, to thereby obtain excellent optical performance, it is important to appropriately set the lens configuration of each of the lens units forming the zoom lens, a refractive power of each of the lens units, a zoom type of the zoom lens, and the like. Moreover, the use of an aspherical lens facilitates the correction of the various aberrations.
However, in order to reduce the occurrence of the various aberrations with the use of the aspherical lens, simply using the aspherical lens is insufficient and it is important to appropriately set a position of the aspherical surface in the optical system, a lens to which the aspherical surface is applied, an aspherical surface amount of the aspherical surface, and the like. If those configurations are not appropriate, it is extremely difficult to obtain the high optical performance over the entire zoom range while downsizing the zoom lens and achieving the higher zoom ratio.